Deflection yoke



May 2l, 195,7 H. THOMAS DEFLECTION YoxE 2 Sheets-Sheet l Filed April 181951 Fig. 4

. INVEN TOR. HARR Y THOMAS A TTORNEY May 21, 1957 vH. THOMAS DEFLECTIONYoxa 2 shears-sheet 2 Filed April 18 .1.951-

INVENTUR. HARRY THOMAS United States Patent O DEFLECTION YOKE HarryThomas, Glen Rock, N. J., assgnor to Allen B.

Du Mont Laboratories, Inc., Passaic, N. J., a corporation of DelawareApplication April 18, 1951, Serial No. 221,590

3 Claims. (Cl. 313-76) This invention relates to electron-beamdeflection means adaptable for use with cathode-ray tubes, andparticularly to magnetic deflection yokes capable of producingwide-angle deflection of an electron beam.

It is desirable to produce a wide angle of electronbeam deflection incertain devices, such -as in certain television cathode-ray picturetubes of the larger sizes. For example, a thirty-inch diametertelevision picture tube such as the type 3013134 requires a deflectionangle of 90 degrees whereas prior tubes of smaller sizes have beendesigned to operate with a beam-deflection angle of only 70 degrees orthereabouts. Larger deflection angles are required in the largertelevision picture tubes in order to reduce `the overall tube length.Accordingly, it is an object of the present invention to provide adeflection means which will enable cathode-ray tubes to have relativelylarger diameters and shorter lengths than heretofore.

Another object is to provide a wide-angle magnetic de flection means forcathode-ray tubes.

A further object is to `avoid neck cut-off of an electron beam in acathode-ray tube.

An additional object is to incorporate means in a magnetic deflectionyoke which will cooperate to effect a displacement of the magneticfield.

A nal object is yto accomplish the above-recited objects with a minimumof distortion effects and with a maximum optimum sensitivity ofdeflection.

Still other objects will become apparent from the following disclosureand claims.

In accordance with the invention, the above-recited objects are realizedby a combination of magnetic fieldshaping devices which are incorporatedin the design of a magnetic deflection yoke. The said devices cooperateto displace the effective concentration of magnetic flux in a forwarddirection toward the screen of a cathoderay tube on the neck of whichthe yoke is placed in the customary manner. The magnetic field is causedto bulge from the yoke in the forward direction in which the electronbeam moves toward the viewing screen.

The invention will be understood in greater detail by reference to thedrawing, in which Fig. l is a perspective view of a deflection yokeconstructed yaccording to the invention,

Fig. 2 is a longitudinal sectional view of the invention applied to acathode-ray tube,

Figs. 3 and 4 are cross-sectional views of the device.

Fig. 5 shows a partial wiring diagram of the invention,

Figs. 6 and 7 show a feature of the invention, and

Figs. 8-12 show representative magnetic iiux patterns produced with andwithout a deflection yoke embodying the present invention.

As shown in the drawing, a deflection yoke 11 is positioned on the neck12 of a cathode-ray tube 13 which contains an electron gun 14 thatprovides an electron beam 16 which impinges upon a viewing screen 17.The yoke 11 comprises an arrangement 1S of deflection ycoils 2,793,311Patented May 21, 1957 having front flares 19 and rear flares 2), atapered liner 21 positioned between the coils 18 and the tube neck 12, atapered core 22 surrounding the outer periphery of the coils 18, a clamp23 surrounding the outer periphery of the core 22, and a rear fringeilux compensating device 24 positioned adjacent the rear ares 20. Thefront flares 19 of the coils 18 are extended to conform with the shapeof the bulb 25 of the cathode-ray tube 13. The coil structure 18preferably comprises two pairs of coils for obtaining horizontal andvertical deections of the beam 16, each coil being of a semi-cylindricalshape and the horizontal and vertical pairs being oriented to producemagnetic fluxes at right angles to each other, in a well-known manner.The cathode-ray tube 13 is shown as comprising Va metal cone 26, and aface plate 2'7 and neck 12 and bulb 25 of glass.

The liner 21 may be formed from fibre or other suitable material, and isshaped and arranged to produce an enlarged diameter of the coilarrangement 18 at the front end, i. e. the end nearest the screen 17.The core 22 is made of a permeable material having the usually desirablemagnetic characteristics, and is tapered or shaped and arranged to havea relatively greater mass or volume at the front end of the yoke. Thefront surface 28 of the core 22 is beveled to closely conform with theshape of the front flare 19 of the coil structure 1S. A shoulder 29 maybe provided to obtain better seating of the clamp 23 against the core22. The core 22 may be split longitudinally into two or more sections inorder to facilitate assembly of the yoke.

The rear fringe flux compensating device 24 is a magnetic device whichfunctions to compensate or reduce the rear fringe flux produced by therear flares 20 of the coiis 18.

Fig. 8 shows diagramtnatically the magnetic flux configuration producedby the yoke 11 without the cornpensating device 24; magnetic flux 31includes a front fringe flux 32 and a rear fringe flut 33 which areproduced in part by the front are 19 and the rear flare 20,respectively.

A preferred form of `the rear fringe flux compensating device 24 isshown sectionally in Fig. 4 and schematically in Fig. 5. Thecompensating device 24 comprises a compensating coil 36 positionedadjacent each rear flare 2t) of each of the coils of the coil assembly18. Each compensating coil 36 is preferably connected electrically toits corresponding deflection coil 13 with a polarity such that themagnetic flux produced by each com pensating coil 36 will oppose andcompensate and reduce or eliminate the rear fringe iiux 33.Alternatively, the coils 36 can be connected to a separate source ofcurrent which fluctuates in accordance with any fluctuations of themagnetic eld produced by the rear flares 2G. Fig. 9 illustrates now therear fringe flux 33 of Fig. 8 has been eliminated by the action of therear fringe flux compensating device 24 having compensating coils 36.Al` though the schematic diagram of Fig. 5 shows a series electricalconnection between the compensating coils 36 and the pair of deilectingcoils 18, it is obvious that parallel connections or a series-parallelcombination of connections may be employed.

As an `alternative to the rear fringe iiux compensating device 24 havingcompensating coils 35, said device 24 may comprise an annular ring 37 orcylinder of magneticresponsive material. Referring to Fig. l0, theannular ring 37 compensating device 24 reduces and confines anddisplaces the rear fringe ux 33 from its normal position shown in Fig.8. The annular ring 37 reduces the magnitude of the fringe flux 33 inthe neck 12 by short-cir cuiting or shunting and deviating the iiux,from its normal path through the neck 12 of the tube 13, to a new pathof circular configuration through the contines of 3 said annular ring37. Any remaining fringe flux 33 within the neck 12 of the tube 13 isdisplaced in a forward direction toward the screen 17, by the action ofthe annular ring 37. (Refer to Fig. l0.) The annular ring 37 ispreferably formed from powdered or laminated magnetic-responsivematerial such as iron.

Although the rear fringe ux compensating device 24 is shown in apreferable position behind and adjacent the rear flares 20, it is to beunderstood that said device 24 may also be positioned in a manner tosurround the periphery of said flares 20, and in certain situations itmay be positioned immediately in front of the rear ares 20.

The coils comprising the coil structure 18 are formed in a certain shapeas shown in Figs. 6 and 7. Fig. 6 shows an individual deflection coil 41positioned on the neck 12 of the cathode-ray tube 13. The remainingcoils comprising the coil structure 1S are not shown. The coil 41 may bewound in the usual manner with a continuous piece of conductive wirelooped to form side portions 42 and 43 and end portions of front andrear flares 19 and 20. A feature of the present invention is thedistribution and spacing of the side portions 42 and 43 to form awedge-shaped window 44 having a greater width at its end near Ithe frontflare 19. Fig. 7 shows the ux pattern produced by a deflecting coilshaped in this manner. The magnetic ilux 31 is displaced and made tocurve and bulge outwardly from the coil 41 at its front end where thegreatest width of the tapered window 44 is located.

In accordance with the present invention, a deflection yoke is producedhaving several features which cooperate to produce a magnetic ilux 46(Fig. l2) which has an etfective center Y that is displaced toward thefront of the yoke from its normal position X (Fig. 1l). For cxample, ayoke without the features of the present invention will have a center ofdeection, denoted by X in Figs. 2 and ll, somewhat near the geometricalcenter of the yoke; the maximum deection angle of a normallydeflectedelectron beam 47 is limited by the neck cut-off point 48 at the junctureof the neck 12 and bulb 25. When a yoke is employed which utilizes thepresent invention, the center of deflection is shifted forward to aposition indicated by Y in Figs. 2 and 12; the maximum deflection angleof a wide-angle-deected electron beam 49 -isvnot so severely limited bythe neck cut-off point 48 a-s is the normally-dellected electron beam47. The center of deecton, such as X or Y, is found by extendingrearwardly the axis of the deflected beam, such as 47 or 49, until itintersects the axis of the undeected beam 16. For simplicity, theelectron beam is shown deflected in only one direction from its originalaxis.

As is illustrated in Fig. l2, the invention causes an active magneticflux to be produced in front of and beyond the contines of the yoke, theterm active distinguishing this ilux from a relatively weak fringe fluxthat normally exists beyond the confines of the yoke.

The tapered liner 21 effects a forward iux displacement due to theaccompanying physical tapered configuration of the coils 18. Therelatively long front flare 19 causes a forward llux displacement byeffecting a forward extension of the coils 18. It has been found thatthe combined effects of the tapered liner 21 and front flare 19 producea greater forward displacement of the center of deection than would beobtained from a summation of the displacements produced individually bythese factors. The reason for this desirable effect is, it is believed,in part due to the fact that the tapered liner causes a less acute anglebetween the front flare 19 and body portion of the coils 18. The frontare thus becomes more nearly in line with the body portion and operatesmore eciently and produces a stronger magnetic field having greaterlateral vector components at the forward part of the yoke than can beobtained if the front are isformed at the normally more acute angle.Also,

the tapering of the coil 18 permits the rear flare 20 to have a moreacute angle with respect to the body portions of said coils 1S, therebyreducing the rear fringe ux.

The tapered magnetic core 22 provides a greater magnetic permeance atthe front of the yoke where the fluxproducing elds have been increasedand aids in obtaining more fully the effects of increased magnetic fluxin and beyond the front portion of the yoke. The Itapered core 22 also-serves to distribute the ux produced along the coils 18 so as toproduce a concentration of flux toward the thick end of the core at thefront end 0f Ithe yoke. r[hese effects result in a wider angle ofdeflection due to a forward displacement of the center of deection. ithas been found that, for a typical yoke, a twentythousandths of an inchforward displacement of the center of deliection resulted in aone-degree increase in deflection angle.

While the present invention has been particularly described with respectto a preferred embodiment, it is realized that modications may be madewithin the scope and teachings disclosed herein; also, subcombinationsmay sometimes be employed when the full effect of the invention is notrequired. The scope of the invention is defined by the following claims.

What is claimed is:

1. A deection coil comprising a plurality of turns of an electricalconductor, said turns shaped to form a pair of side portions and frontand rear are portions; a window area bounded by said side portions andboth said are portions; said pair of side portions being unequallyspaced from each other along their inner edges, said unequal spacingbeing smallest at said rear are portion and greatest at said front areportions; said side portions being narrowest at said front flare portionand widest at said rear flare portions; the outer edges of each of saidside portions being equally spaced along the length thereof.

2. A deflection yoke comprising a cylindrical structure of deflectioncoils, each of said coils being made from an electrical conductor shapedto form a pair of side portions and flare portions which define andbound a window area, the side portions of each said pair thereof beingunequally spaced from each other along their inner edges, said unequalspacing being the greatest at one end of said coil structure and saidside portions being narrowest at said one end of the coil structure, theouter edges of said side portions of each pair thereof being equallyspaced apart along the length thereof, a core formed of material havingmagnetic permeance positioned around the periphery of said coilstructure and having its greatest magnetic permeance at said one end ofsaid coil structure, means to energize said coils to produce magneticfields, and a flux compensating device positioned adjacent said areportions at the remaining end of said coil structure whereby said fluxmass is effectively shifted away from said remaining end and toward saidone end.

3. A deflection yoke comprising a cylindrical structure of deflectioncoils, said coils having laterally extending flares at an end of saidcylindrical structure, a core formed of material having magneticpermeance positioned around the periphery of said coil structure andhaving its greatest magnetic permeance at the end thereof remote fromsaid flares, means to energize said coils to produce magnetic fields,and a ux compensating device positioned adjacent said flares.

References Cited in the le of this patent UNlTED STATES PATENTS2,151,530 Ruska Mar. 2l, 1939 2,172,733 Frederrnann et al Sept. 12, 19392,186,595 Fuska Ian. 9, 1940 2,207,777 Blain July 16, 1940 21,227,080Goldsmith Dec. 31, 1940 (Other references on following page) 5 Gunther Ian. 7, 1941 Bruche Apr. 8, 1941 Gunther Sept. 29, 1942 Flechsig June 1,1943 Bedford Dec. 14, 1943 De Tar June 8, 1948 Haantjes Nov. 30, 1948Bocciarelli Dec. 14, 1948 6 Torsch Jan. 10, 1950 Bocciarelli Oct. 9,1951 Neeteson Nov. 4, 1952 Lawrence Nov. 25, 1952 OTHER REFERENCES July17, 1951.

